RCA cabient from scratch and help needed on the next steps

Posted: 1/19/2007 2:12:15 PM
mikebuffington

From: AZ

Joined: 11/25/2005

I have completed (to a point of showing my progress with photographs) the machining of replica RCA theremin antenna. I have completed two sets and am close to completing 2 more.

Many photos of bending the volume loop and cutting the nuts, the antenna mounts, and antenna bases can be found at:

http://bedsidestory.livejournal.com/36774.html

There's lots of photos, so it might take a while to load.
Posted: 1/19/2007 11:43:33 PM
kenbarbdae

From: south carolina

Joined: 12/7/2005

Great job on the the antennae! Please tell me you have an extra set to sell - my theremin is still missing both and I've held off finding a set until I got the cabinet restored. Let me know if you plan to offer them for sale.
Posted: 1/20/2007 1:40:49 AM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

Mike - Thanks so much for sharing the photo journal. It's great for everyone to see exactly what's involved in the process.

I take it you did the machining work yourself? If so, it probably saved you a pretty penny.

I know the brass is not cheap. This past September I had a professional machinist make fittings for three sets of antennas. Even though he said he was giving me a break, I was surprised at what it cost me. Now I know why Floyd Engels is asking so much for the sets he had made.

I still need to bend the tubing, if I ever get the chance to cut my working hours down to a reasonable level. It is very helpful to see your jig and have the benefit of your experience. I would appreciate it if you would explain the procedure you used to anneal the tubing. (By the way...is it brass or copper?)

I didn't have the nuts made because I had the more common 5/8"-27 threads cut. (The same as a microphone mount.) The nuts are available from McMaster-Carr.

Here are a couple of pictures of my fittings. (I hope this works!)

Fittings Group (http://new.photos.yahoo.com/jaygeeess/album/576460762354675916/photo/294928804188330192/0)

Fittings (http://new.photos.yahoo.com/jaygeeess/album/576460762354675916/photo/294928804188338950/1)
Posted: 1/20/2007 1:59:42 AM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

PS....The one mistake I made was that I got greedy and bought 0.010" slit saw blades.

One piece is slightly damaged from one of the blades binding and breaking. The saw cuts on the other pieces are a little crooked because the blade was so thin it would wander a bit.
It turns out that as you make the saw cuts the brass wants to close up on you apparently from the stress in the material being relieved.

If I were to do it again, I would recommend using a slit saw blade of at least 0.015" or possibly 0.020" but no larger. These pieces are not very big to begin with, as you well know.

But that's all right because they are all functional and the "damage" will be hidden anyway.
Posted: 1/20/2007 3:05:08 AM
mikebuffington

From: AZ

Joined: 11/25/2005

Jeff,

Thanks for showing your pictures. It's nice to see pieces that look the same!

I am obsessing over details and micrometers and at the same time I have been wishing for more control on the lathe. An eighth of a turn, a bump of a handle, turning the wrong handle only just a bit, etc. can cause the piece to be almost worthless. I imagine CNC turned pieces and drool over that imaginary precision. At least I know RCA wasn't using them.

This was really my first time turning metal on a lathe. It is hard work, and worth it. I did save money, but also had to buy enough stock, and a few tools. Thank goodness for good, trusting friends with tools!

In my photo of the tube on the white bricks, those bricks are fire bricks from a kiln. They're good to trap and reflect the heat, and make everything even when annealing. I had help torching the rod with portable torches: one person passing slowly over the brass from the outside in, meeting in the center, and not moving in until the section you were hovering over was a nice dark cherry red. It's good to get the hottest part of the torch right over the brass. It was helpful to anneal in a non-well lit room so you can see the glow. You can quench the tubing in water, or just let it cool by putting it on cold steel or concrete and letting it sit. I found the less handling caused less dings. It's not easy managing a glowing hot tube of brass. The brass will then be workable. The hand bending was pretty easy. I would not use any mallets or clamps, or you might get some marring and crimping.

The tubing is brass 260 (only O.D./thickness match at McMaster-Carr) and the solid brass is brass 360

I have not cut the slits yet. It's nice to know a good thickness to use. I wonder if using a jeweler's saw will be more precise than a slit saw. I assume you're using the slit saw blade on a milling machine?

Oh, it seems that the annealing will expand the metal a bit, so the base piece that oh-so-perfectly fits in the pitch antenna tube will probably not fit that way in the loop antenna tube. I am holding off on trying to get those pieces to fit until I have done more tube work. Also using a pipe cutter will squeeze in the wall a bit. It's nice to face off the straight pitch tube on the lathe, but you can't have that option on both ends of the bent loop tube. One side can be faced off and cleaned up before you put it in the jig, though (make sure that jig is pretty precise if you attempt that).


Ken,

Two of the four are spoken for, and the third is up in the air right now. After I finish and plate everything, I'll post here or contact you.
Posted: 1/20/2007 10:42:46 AM
Dayfan

Joined: 10/8/2005

Liked your step-by-step photos. Looks like a very professional job with the attention to detail that this type of project deserves. I liked your bending jig also. I'm glad to see that the Deserving are using the info on the RCA that is now available.

Mark
Posted: 1/20/2007 5:57:39 PM
kenbarbdae

From: south carolina

Joined: 12/7/2005

Sounds great Mike. You can contact me at
kenbarbdae(at)yahoo.com. Looking forward to hearing from you and seeing your finished project!
Posted: 2/23/2007 10:20:50 PM
organ man

From: Kalamazoo, MI

Joined: 3/20/2006

Hey all,

I'm working on my antennae fittings right now and... what the heck is the point in cutting slits in those antennae bases? How are they supposed to stay in the case fittings?

ba
Posted: 2/23/2007 10:57:01 PM
mikebuffington

From: AZ

Joined: 11/25/2005

The slits allow for some give so that the bases sit in the mounts nice and firm. The bases should be ever so slightly larger ( like 0.313 inches) in diameter than the 5/16 drilled hole.

I like the cabinet image I see for your avatar! Looks great! Do you have larger photos you can share?
Posted: 2/24/2007 10:05:07 PM
organ man

From: Kalamazoo, MI

Joined: 3/20/2006

thanks for your quick reply and compliment Mike. I do have some larger photos but haven't don't have any sort of website to post them to at the moment. I would just have to email them to you. My email is: baldrich@iserv.net. Send me a message and I'll send you some photos.

So the antennae are a press fit, so to speak? ok. Where and how do the wires to the coils attach then?

ba

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